Tape media kiss-contact read verification

ABSTRACT

A supplemental module that includes one or more read elements periodically engages a magnetic recording medium, and the read elements generate an electrical signal corresponding to transitions written to the magnetic recording medium by a write element. A computer receives information representative of the electrical signal and determines if a quality metric of the magnetic recording medium derived from the electrical signal is within a defined range. If the quality metric is not within the defined range, a defined action is performed by the computer.

FIELD OF THE INVENTION

The present invention relates generally to the field of magneticinformation storage and retrieval, and more particularly to determiningsignal characteristics from recorded data on a magnetic recording mediato determine quality metrics associated with the media and recordeddata.

BACKGROUND OF THE INVENTION

Archival recording to tape and other magnetic media may require that themagnetic media be written with a high degree of quality to satisfyauditing, retention, and other mission critical requirements. Forexample, the write quality on master or reference tapes in the media andentertainment industry may be extremely critical. Typical tape drivesand other tape recording appliances are not configured to accuratelydetermine when writing degrades, but is still within an acceptablerange.

SUMMARY

Embodiments of the present invention disclose a method and apparatus fordetermining quality metrics of a magnetic recording medium. Asupplemental module that includes one or more read elements periodicallyengages a magnetic recording medium, and the read elements generate anelectrical signal corresponding to transitions written to the magneticrecording medium by a write element. A computer receives informationrepresentative of the electrical signal and determines if a qualitymetric of the magnetic recording medium derived from the electricalsignal is within a defined range. If the quality metric is not withinthe defined range, a defined action is performed by the computer.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1A is a functional block diagram illustrating a tape recordingappliance, in accordance with an embodiment of the present invention.

FIG. 1B illustrates an exemplary tape cartridge, in accordance with anembodiment of the present invention.

FIG. 2A illustrates a side view of a read/write head, in accordance withan embodiment of the invention.

FIG. 2B illustrates a side view of a read/write head, in accordance withanother embodiment of the invention.

FIG. 3 illustrates a representative tape bearing surface of a module, inaccordance with an embodiment of the present invention.

FIG. 4 illustrates read and/or write element arrays, in accordance withan embodiment of the present invention.

FIG. 5 illustrates a representative partial tape bearing surface,illustrating a read/write element array in additional detail, inaccordance with an embodiment of the present invention.

FIG. 6A illustrates construction of a read element, in accordance withan embodiment of the present invention.

FIG. 6B illustrates construction of a read element, in accordance withanother embodiment of the present invention.

FIG. 7 is a flowchart depicting operational steps that a microprocessormay perform, in accordance with an embodiment of the invention.

FIG. 8 illustrates a block diagram of components of a host, inaccordance with an embodiment of the present invention.

DETAILED DESCRIPTION

The present invention is directed generally to magnetic storage devices,such as tape appliances, that include a supplemental read module, inaddition to the regular “production” read/write modules of a read/writehead, that is used for determining the performance characteristics andquality metrics of the write elements in the regular read/write modulesand recorded magnetic media. Tape drives, for example, typically includemechanisms to ensure that data is accurately written to tape. However,some of these mechanisms, such as error recovery, may mask problems thatmay be occurring at the write elements. For example, a tape driveperforming a read-after-write operation may detect an error, andautomatically rewrite the data to the tape. If the cause of the dataerror is degradation of a write element, the degradation may have toprogress substantially before the error rate is considered unacceptable,and a notification is generated by the tape drive. While degradation isprogressing, effective write speeds and data density may be worsening.These secondary effects may be the first indication that written dataquality is deteriorating.

While poor overall quality of data written to a magnetic medium may notbe efficient, as long as the data can be read, the poor quality maysatisfy data retention requirements mandated by statute, policies, orprocedures. However, certain archival applications, such as the creationof master or reference tapes in the media and entertainment industry,may require, for example, by contract, that the data written to anarchival tape be of very high quality. Such quality may be defined bymetrics such as a low bit error rate (BER), high signal-to-noise ratio(SNR), high magnetic field strength of data recorded to the magneticmedium, a small transition parameter, a small PW50 pulse width, a highdegree of overwrite, and/or other metrics that are known in the industryor defined by agreement. The quality levels defined by agreement may besignificantly more stringent than the acceptable levels of the magneticrecording device, as may be defined by standards and/or specifications,such as ECMA-319. It would be advantageous to have a system that candetect degradation of the write quality of a write element before thedegradation has progressed to the point that the data quality is out ofspecification.

In embodiments of the invention, a supplemental module that includes aread element array periodically engages a magnetic medium, such as amagnetic tape, and reads data, such as production data or test patters,and erased media, from data tracks to determine the quality of the writeelements in the production read/write modules. The supplemental readmodule may periodically “kiss” the magnetic medium, via, for example, aprecision servo system that moves the module or the magnetic medium.Information determined from the electrical signals generated by the readelements may be used to detect and determine the performance of thewrite elements, or the read/write element arrays in which the writeelements are disposed. Because the supplemental module is onlyperiodically in contact with the magnetic medium, the performancecharacteristics of the supplemental module and its read elements are notexpected to change or degrade appreciably over the life of the magneticstorage device, or another defined time period. In certain embodiments,a coating may be applied to the read element array of the supplementalmodule, and/or the read elements may be recessed, so as to force adefined separation between the read elements and the tape. This mayforce an extra degree of spacing loss in the magnetic field strengthdetected by the read elements such that the signal resolution may beclose to the minimum acceptable value, and may be used to detectsub-optimal, but within specification, performance of the read/writeelement arrays of the other read/write modules. A better understandingof certain aspects of the embodiments presented herein may be gained byreference to U.S. patent application Ser. No. 13/741,352, filed Jan. 14,2013, which is hereby incorporated herein by reference in its entirety.

While embodiments of the invention are described with respect to a tapeappliance and a magnetic tape medium, those of skill in the art willrecognize that the inventive concepts described herein may beimplemented in embodiments directed to related magnetic storagetechnologies, such as hard disk drives (HDDs), without undueexperimentation, and without departing from the spirit of the invention,and these are, therefore, considered to be within the scope of theinvention, as defined in the claims below.

For purposes of the description hereinafter, the terms “upper”, “lower”,“right”, “left”, “vertical”, “horizontal”, “top”, “bottom”, “outer”,“inner”, and derivatives thereof shall relate to the disclosedstructures and methods, as oriented in the drawing figures. The terms“overlying”, “atop”, “on top”, “positioned on” or “positioned atop” meanthat a first element, such as a first structure, is present on a secondelement, such as a second structure, wherein intervening elements, suchas an interface structure may be present between the first element andthe second element. The term “direct contact” means that a firstelement, such as a first structure, and a second element, such as asecond structure, are connected without any intermediary conducting,insulating or semiconductor layers at the interface of the two elements.

FIG. 1A is a functional block diagram of a tape appliance 100, inaccordance with an embodiment of the invention. In an exemplaryembodiment, tape appliance 100 may be a tape drive. Tape appliance 100may include several components providing a control and data transfersystem for reading and writing data from a host CPU 102, an embodimentof which is described below in relation to FIG. 8, on a magnetic tapemedium. By way of example only, those components may include a channeladapter 104, a computer, such as microprocessor controller 106, a databuffer 108, a read/write data flow circuit 112, a motion control system110, and a tape interface system 114 that includes a motor drivercircuit 116 and read/write heads 118.

Microprocessor controller 106 may provide overall control functionalityfor the operations of all other components of tape appliance 100. Thefunctions performed by microprocessor controller 106 may be programmablevia microcode routines (not shown) according to desired tape driveoperational characteristics. During data write operations (with alldataflow being reversed for data read operations), microprocessorcontroller 106 activates channel adapter 104 to perform the requiredhost interface protocol for receiving an information data block. Channeladapter 104 communicates the data block to the data buffer 108 thatstores the data for subsequent read/write processing. Data buffer 108 inturn communicates the data block received from channel adapter 104 toread/write dataflow circuitry 112, which formats the device data intophysically formatted data that may be recorded on a magnetic tapemedium. Read/write dataflow circuitry 112 is responsible for executingall read/write data transfer operations under the control ofmicroprocessor controller 106. Formatted physical data from read/writecircuitry 112 is communicated to tape interface system 114. The latterincludes one or more read/write modules in read/write head unit 118, anddrive motor components (not shown) for performing forward and reversemovement of a tape medium 120 mounted on a supply reel 122 and a take-upreel 124. The drive components of tape interface system 114 arecontrolled by motion control system 110 and motor driver circuit 116 toexecute such tape movements as forward and reverse recording andplayback, rewind and other tape motion functions. In addition, inmulti-track tape drive systems, motion control system 110 transverselypositions read/write heads 118 relative to the direction of longitudinaltape movement in order to record data in a plurality of tracks.

In certain embodiments, during read operations, microprocessorcontroller 106 may receive the unformatted electrical signals from tapeinterface system 114, either directly or via read dataflow circuitry112. In other embodiments, read dataflow circuitry 112 may performvarious pre-processing functions on the electrical signals from tapeinterface system 114, and transmit information that is representative ofthe electrical signals to microprocessor controller 106. In theseembodiments, microprocessor controller 106 may include appropriateelectrical circuitry, logic, firmware, software, etc., to performanalysis of the electrical signals or information to determine variouscharacteristics of the signals related to quality of the recorded dataand the magnetic medium, in accordance with embodiments of theinvention. In general, the appropriate electrical circuitry, logic,firmware, software, etc., to perform analysis of the electrical signalsto determine various characteristics of the signals related to qualityof the recorded data and the magnetic medium may be located in one ormore functional components of a tape appliance, such as tape appliance100, and/or in a host computer, such as host CPU 102.

FIG. 1B illustrates an exemplary tape cartridge 150 according to anembodiment. Tape cartridge 150 may be used with a system such as tapeappliance 100 shown in FIG. 1A. As shown, tape cartridge 150 includes ahousing 152, a tape 120 in the housing 152, and a nonvolatile memory 156coupled to the housing 152. In some embodiments, the nonvolatile memory156 may be embedded inside the housing 152. In other embodiments, thenonvolatile memory 156 may be attached to the inside or outside of thehousing 152 without modification of the housing 152. For example, thenonvolatile memory may be embedded in a self-adhesive label 154. In onepreferred embodiment, the nonvolatile memory 156 may be a flash memorydevice, ROM device, etc., embedded into or coupled to the inside oroutside of the tape cartridge 150. The nonvolatile memory may beaccessible by tape appliance 100, and the tape operating software (thedriver software) residing on host CPU 102. In an exemplary embodiment,tape cartridge 150 meets the standards specifications of one or more ofthe Linear Tape Open (LTO) generations, such as LTO-6. All trademarksused herein are the property of their respective owners. In such anembodiment, supply reel 122 may be integral to the LTO tape cartridge,and the end of tape 120 includes a leader pin (not shown) which ismechanically grasped by features (not shown) of tape interface system114 and threaded onto tape-up reel 124.

FIG. 2A illustrates a side view of a read/write head 118 in accordancewith an embodiment of the invention. Read/write head 118 includes first,second and third modules 204, 212, and 208, respectively, mounted tobases 202, 210, and 206, respectively. The bases may be “U-beams” thatare physically coupled together. First, second and third modules 204,212, and 208 each have a tape bearing surface 220, 224, and 222respectively, which may be flat, contoured, etc. Each module 204, 212,and 208 may be configured for writing and/or reading data, for example,data received from or transmitted to host CPU 102, to and from a tape234. Modules 204, 212, 208 may receive data for writing and transmitdata that is read via cables 226, which may couple the modules to readdataflow circuitry 112. Note that while the term “tape bearing surface”appears to imply that the surface facing tape 234 is in physical contactwith the tape bearing surface, this is not necessarily the case. Rather,only a portion of the tape may be in contact with the tape bearingsurface, constantly or intermittently, with other portions of the tape“flying” above the tape bearing surface on a layer of air, usuallyreferred to as an “air bearing.” By way of explanation, first module 204can be referred to as the “leading” module as it is the first moduleencountered by tape 234 when moving from left to right, as illustrated.Second module 212 can be referred to as the “middle” module, and thirdmodule 208 can be referred to as the “trailing” module. The leading andtrailing modules 204 and 208, respectively, are referred to collectivelyas outer modules. Note that outer modules 204 and 208 will alternate asleading modules, depending on the direction of travel of the tape 234.

In an exemplary embodiment, closures 214, 218, and 216 are attached tomodules 204, 212, and 208, respectively, and serve to extend tapebearing surfaces 220, 224, and 222, and to define gaps at the junctionsof the modules and closures in which tape read and write elements,described in more detail below, are disposed. Locating the read andwrite elements interior to the edges of the tape bearing surfaces mayserve to reduce wear and tear of the read/write elements resulting fromdirect contact from tape 234. Modules 204, 212, and 208, and closures214, 218, and 216 may be made of a wear resistant substrate material,such as a ceramic. In some embodiments, middle module 212 has a closure,while the outer modules 204, 208 do not. Where there is no closure,preferably a hard coating is added to the module. One preferred coatingis diamond-like carbon (DLC).

In one embodiment, tape bearing surfaces 220, 224, and 222 of the first,second and third modules 204, 212, and 208, respectively, lie onapproximately parallel planes, with tape bearing surface 224 of themiddle module 212 being slightly above tape bearing surfaces 220 and 222of the outer modules 204 and 208. As described below, this has theeffect of creating a desired wrap angle α₂ of the tape relative to thetape bearing surface 224 of the middle module 212.

Tape bearing surfaces 220 and 222 may include sharp outer edges, or“skiving” edges, where tape 234 will first contact tape bearing surfaces220 and 222 when either outer module 204 and 208 is the leading module.The skiving edges serve to “shear” air from the underside of tape 234 toprevent air from being drawn into the head-tape gap by the tape, so thatatmospheric pressure may push the tape into substantially full contact,i.e., with a small tape fly height, over the longitudinal dimension,with respect to tape direction, of the tape bearing surfaces. A smallamount of roundness or slope at the incoming edge may generate anunacceptably thick air bearing, separating the tape from the head, andits read/write elements, as described below, and present problems inreading and writing high density recordings due to spacing loss effects.

Where the tape bearing surfaces 220, 224, and 222 lie alongapproximately parallel offset planes, the vacuum created by the skivingedge of tape bearing surface 220 of the leading module 204 results inthe trailing edge of tape bearing surface 220 (the edge from which thetape leaves the leading module 204) being the approximate referencepoint which defines the wrap angle α₂ over the tape bearing surface 224of the second module 212. Because the tape stays in close proximity totape bearing surface 220 until close to its trailing, read and/or writeelements, described in more detail below, may be located near thetrailing, or inner, edges of the outer modules 204, 208.

A benefit of this and similar embodiments is that, because the tapebearing surfaces 220 and 222 of outer modules 204, 208 are fixed at adetermined vertical offset from the tape bearing surface 224 of themiddle module 212, the inner wrap angle α₂ is fixed when modules 204,212, and 208 are physically coupled together or are otherwise fixed intoa head assembly. The inner wrap angle α₂ is approximately tan−1(δ/W)where δ is the height difference between the planes of the tape bearingsurfaces 220 and 224, and W is the width between the opposing ends ofthe tape bearing surfaces 220 and 224. An illustrative inner wrap angleα₂ is in a range of about 0.5° to about 1.1°, though can be any anglethat is advantageous to a design. Beneficially, the inner wrap angle α₂on the side of middle module 212 receiving the tape (leading edge) willbe larger than the inner wrap angle as on the trailing edge, as the tape234 rides above tape bearing surface 222 of trailing module 208. Thisdifference is generally beneficial as a smaller as tends to oppose whathas heretofore been a steeper exiting effective wrap angle.

Note that the tape bearing surfaces 220, 222 of the outer modules 204,208 are positioned to achieve a negative wrap angle at the trailing edgeof the tape bearing surface 220 of the leading module 204. This isgenerally beneficial in helping to reduce friction due to contact withthe trailing edge, provided that proper consideration is given to thelocation of the “crowbar” region, where the tape forms a slight bubble,that forms in the tape where it peels off the head. This negative wrapangle also reduces flutter and scrubbing damage to the elements onleading module 204. Further, at trailing module 208, tape 234 flies overthe tape bearing surface 222 so there is virtually no wear on theelements when tape is moving in this direction. Particularly, tape 234entrains air and so will not significantly ride on the tape bearingsurface 222 of the trailing module 208 (although some contact mayoccur). This is permissible in certain embodiments, for example, wherethe leading module writes onto the tape, the middle module may perform aread-after-write function, and the trailing module 208 is idle.

Writing and reading functions may be performed by different modules atany given time. In one embodiment, middle module 212 includes aplurality of data and optional servo readers and no data writers. Outermodules 204, 208 may include a plurality of writers and no readers, withthe exception that outer modules 204, 208 may include optional servoreaders. The servo readers may be used to laterally position the head,with respect to tape direction, during reading and/or writingoperations.

In the embodiment illustrated in FIG. 2A, first, modules 204, 212, 208each have a closure 214, 218, 216, which extends the tape bearingsurface of the associated module, thereby effectively positioning theread/write elements away from the edge of the tape bearing surface.Closure 218 on second module 214 can be a ceramic closure of a typetypically found on tape heads. The closures 214, 216 of the outermodules 204, 208, however, may be shorter than closure 218 of secondmodule 212 as measured parallel to a direction of tape travel over therespective module. This enables positioning the modules closer together.One way to produce shorter closures 214, 216 is to lap the standardceramic closures of the second module 212 an additional amount. Anotherway is to plate or deposit thin film closures above the elements duringthin film processing. For example, a thin film closure of a hardmaterial such as Sendust or nickel-iron alloy (e.g., 45/55) can beformed on the module.

With reduced-thickness ceramic or thin film closures 214, 216 or noclosures on the outer modules 204, 208, the write-to-read gap spacingcan be reduced to less than about 1 mm, e.g., about 0.75 mm, or 50% lessthan standard LTO tape head spacing. The open space between the modules204, 212, 208 can still be set to approximately 0.5 to 0.6 mm, which insome embodiments is ideal for stabilizing tape motion over the secondmodule 212.

In alternative embodiments, depending on tape tension and stiffness, itmay be desirable to angle the tape bearing surfaces of the outer modulesrelative to the tape bearing surface of the middle module. For example,the tape bearing surfaces of the outer modules may be about parallel tothe tape at the desired wrap angle α₂ of the middle module. In otherwords, the planes of the tape bearing surfaces of the outer modules areoriented at about the desired wrap angle α₂ of the tape relative to themiddle module. The tape will also pop off of the trailing module in thisembodiment, thereby reducing wear on the elements in the trailingmodule. These embodiments are particularly useful for write-read-writeapplications. Additional aspects of these embodiments are similar tothose given above.

In operation, as tape 234 passes over the read and write elements intape bearing surfaces 220, 224, 222 of read/write head 118, motioncontrol system 110 transversely positions read/write heads 118 relativeto the direction of longitudinal tape movement in order to read datafrom or write data to the data tracks in a particular data band of tape234, as will be described in more detail below.

Read/write heads 118 also includes a supplemental module 230 on a mount228. A cable 226 may couple supplemental module 230 to read dataflowcircuitry 112 for transmitting data read by or to be written by thesupplemental module. In certain embodiments of the invention,supplemental module 228 is coupled to the modules of read/write heads118 such that supplemental module 230 follows the lateral movements ofmodules 204, 212, 208, and additionally may independently move at leastalong an axis perpendicular to the plane of the tape above tape bearingsurface 232 of the supplemental module. Generally, this movement can bereferred to as “vertical” movement. Thus, although the vertical movementof supplemental module 230 may not be strictly perpendicular to theplane of the tape above the supplemental module, at least one componentof the movement is perpendicular to the plane of the tape, such thatvertical movement of module 230 will bring tape bearing surface 232, andthe read elements therein, as described in more detail below, into andout of engagement with tape 234.

Actuation of the vertical movement of supplemental module 230 may beperformed, for example, by a precision servo mechanism 236 coupled tobase 228 of supplemental module 230, controlled by motion control system110 and microprocessor controller 106, and, optionally by host CPU 102.To ensure that supplemental module 230 precisely follows the lateralmovements of modules 204, 212, 208, base 228 of the supplemental modulemay, for example, be coupled directly to base 206, via atongue-and-groove arrangement, a dovetail-rail arrangement, or anothersuitable structure or arrangement that allows vertical movement ofsupplemental module 230 while ensuring that supplemental module 230precisely follows the lateral movements of modules 204, 212, 208. Base228 may alternatively, or additionally, be indirectly coupled to modules204, 212, 208 by, for example, being coupled to a common supportstructure. For example, the axis of vertical movement of supplementalmodule 230 may be controlled by a shaft- and hole arrangement, with onecomponent integral to the common support, and the other integral to base228. In other embodiments, supplemental module 230 may not be tightlycoupled to modules 204, 212, 208, and may perform track followingfunctions, under control, for example, of motion control system 110,independent of modules 204, 212, 208, as may be known in the art.

In an alternative embodiment, illustrated in FIG. 2B, supplementalmodule 230 may be fixed in relation to modules 204, 212, 208, and tape234 may be lifted off of, or lowered onto, tape bearing surface 232 ofthe supplemental module. For example, a precision controlled roller orguide 238, disposed along the tape path between supplemental module 232and, for example, a capstan/pinch roller assembly (not shown), may liftand lower tape 232, under the control of motion controller 110,microprocessor controller 106, and, optionally, host CPU 102. Withrespect to the aspect of embodiments in which tape 234 periodicallyengages supplemental module 230, this alternative embodiment maysatisfactorily implement this aspect. In a further embodiment, acombination of vertically moving supplemental module 232 and lifting andlowering tape 234 may also satisfy this aspect. In general, anyarrangement which allows for tape 234 to periodically engagesupplemental module 230, in accordance with embodiments of theinvention, may be used.

In certain embodiments, engaging tape 234 with supplemental module 230will not adversely interfere with normal tape read/write operations ofmodules 204, 212, and 208. For example, engaging tape 234 withsupplemental module 230 may affect the wrap angle at the edge of tapebearing surface 222 nearest supplemental module 230. With the tapedirection as indicated, engaging the tape may not affect wrap angles α₁and α₂, as illustrated. Because trailing module 208 is idle when thetape direction is as indicated, engaging the tape may not interfere withnormal tape read/write operations of modules 204 and 212. In contrast,if the tape direction is in the opposite direction to what is indicated,the effect of engaging the tape at the wrap angles at the now-leadingedges of tape bearing surfaces 222 and 218 may adversely affect thenormal tape read/write operations of modules 208 and 212. In thisembodiment, engaging tape 234 with supplemental module 230 might onlyoccur when the tape is moving in the direction indicated.

When supplemental tape 234 is engaged with supplemental module 230,sufficient pressure is exerted by the supplemental module on the tape toensure a satisfactory contact of the tape with tape bearing surface 232,in which read elements are disposed. This pressure may depend on suchfactors as the relative geometries of tape bearing surface 232 and tape234, an acceptable thickness of an air bearing, an acceptable amount ofactual (asperity) contact under pressure between the tape and the tapebearing surface, etc. In various embodiments, the tape pressure on tapebearing surface 232, as well as the tape pressure on tape bearingsurfaces 220, 224, 222, may range, for example from 10 to 100 kPa.

In the embodiment of FIGS. 2A and 2B, supplemental module 230 isillustrated as having at least a partially beveled tape bearing surface232. In other embodiments, tape bearing surface 232 may be planar,and/or may be oriented such that the surface is coplanar, approximatelycoplanar, are at a desired wrap angle, to the plane of tape 234 whentape bearing surface 232 engages tape 234. Other embodiments may includedifferent geometries of tape bearing surface 232, such as flat,contoured, etc., and angles of engagement between tape bearing surface232 and tape 234, to affect, for example, the degree of contact betweentape bearing surface 232 and tape 234.

FIG. 3 illustrates a representative tape bearing surface 224 of module212, from the perspective of a downward view, in accordance with anembodiment of the present invention. A representative tape 234 is shown,with servo tracks 306 indicated in dashed lines, and data bands 304between the servo tracks 306. In this example, tape 234 includes 4 to 22data bands 304, e.g., with 16 data bands 304 and 17 servo tracks 306, ona one-half inch wide tape 234. Each data band may include a number ofdata tracks, for example 1024 data tracks (not shown). Module 204 ispreferably long enough to be able to support tape 234 as the head stepsbetween data bands 304. During read/write operations, read and/or writeelements of read/write element array 302, disposed in a gap 300 of tapebearing surface 224 of module 212 where the tape bearing surface ofclosure 218 abuts module 224, are positioned to specific track positionswithin one of the data bands 304. Outer read elements of read/writeelement array 302, which may be referred to as servo readers, read theservo tracks 306. The servo signals generated by the servo readers andreceived by motion control system 110 are used to align the read and/orwrite elements 302 with a particular set of data tracks duringread/write operations.

FIG. 4 depicts read and/or write element arrays 400, 402, 404, and 412of read/write heads 118, which may be formed, for example, in gaps 300of modules 204, 212, 208, and supplemental module 228. As shown, theread and/or write element arrays may include, for example, 16 readelements 408 or 414, 16 write elements 410, and two servo readers 406,though the number of elements may vary. Illustrative embodiments mayinclude 8, 16, 32, 40, or 64 active read and/or write elements perarray, and alternatively interleaved designs having odd numbers of reador write elements such as 17, 25, 33, etc. An illustrative embodimentincludes 32 read elements per array and/or 32 write elements per array,where the actual number of transducer elements could be greater, e.g.,33, 34, etc. This may allow the tape to travel more slowly, therebyreducing speed-induced tracking and mechanical difficulties and/orexecute fewer “wraps” to fill or read the tape. While the read and writeelements may be arranged in a “piggyback” configuration as shown in FIG.4, for example, in read/write element arrays 400 and 404, the readelements 408 and write elements 410 may also be arranged in aninterleaved configuration. Alternatively, each array of read and/orwrite elements 400, 402, 404 may be read or write elements only, and thearrays may contain one or more servo readers 406. Each module 204, 212,208 may include a complementary set of read and/or write elements forsuch things as bi-directional reading and writing, read-while-writecapability, backward compatibility, etc.

In exemplary embodiments of the invention, read element array 412 isdisposed in tape bearing surface 232 of supplemental module 230. Incertain embodiments, read elements 414 of element array 412 may befabricated differently than, and have difference performancecharacteristics than, read elements 408 of read/write arrays 400, 402,and 404. Read element array may include one or more servo readers 406for reading, for example, servo tracks 306, for transverse positioningof supplemental module 230 with respect to, for example, data bands 304.As indicated in FIG. 4, in certain embodiments, supplemental module 230may also move in a “vertical” direction (into and out of the page asillustrated), as well as in a transverse direction, with respect to thetape direction.

FIG. 5 shows a representative partial tape bearing surface 220 of module204 of read/write head heads 118, from the perspective of a downwardview, illustrating representative read/write element array 400 inadditional detail, in accordance with an embodiment. A read/writeelement array 400 may have a plurality of read/write element (R/W) pairs510 in a piggyback configuration formed, for example, on the substratematerial of module 204 and an optional electrically insulative layer512. The write elements, exemplified by write element 410, and the readelements, exemplified by read element 408, are aligned parallel to thedirection of travel of a tape medium to form a R/W pair 510. Several R/Wpairs 510 may be present, such as 8, 16, 32 pairs, etc. The R/W pairs510 as shown are linearly aligned in a direction generally perpendicularto the direction of tape travel. However, the pairs may also be aligneddiagonally, etc. Servo readers 406 are positioned on the outside of thearray of R/W pairs 510.

Generally, the magnetic tape medium may move transversely acrossread/write element arrays 400, 402, 404, and 412, in either direction,and read/write heads 118 may be moved laterally, with respect to thetape direction, between data tracks and data bands 304 on the tape. Themagnetic tape medium and read and/or write element arrays 400, 402, 404,and 412 operate in a transducing relationship in a manner known in theart.

In an embodiment, when a module is constructed, for example, module 204,layers are formed in the gap 300 created above the electricallyconductive substrate material of module 204 (partially shown), e.g., ofAlTiC, in generally the following order for the R/W pairs 510, andsimilarly for servo readers 406 (however, without the writer poles): aninsulating layer 512; a first shield 500 typically of an iron alloy suchas NiFe, CZT or Al—Fe—Si (Sendust); a sensor 502 for sensing a datatrack on a magnetic medium of any known type, including those based onmagnetoresistance (MR), giant MR (GMR), anisotropic MR (AMR), tunnelingMR (TMR), etc.; a second shield 504 typically of a nickel-iron alloy(e.g., ˜80/20 at % NiFe, also known as permalloy); first and secondwriter pole tips 506, 508, and a coil (not shown). First and secondwriter poles 506, 508 may be fabricated from high magnetic momentmaterials such as ˜45/55 NiFe. In preferred embodiments, due to its highmagnetoresistive change and superior signaling characteristics, at leastsensors 502 of supplemental module 230 are TMR sensors.

Note that these materials are provided by way of example only, and othermaterials may be used. Additional layers such as insulation between theshields and/or pole tips and an insulation layer surrounding the sensormay be present. Illustrative materials for the insulation includealumina and other oxides, insulative polymers, etc. Materials andconstruction of read elements 414, and read element array 412, ofsupplemental module 230 may be directed to a specific generation of tapemedia, and may be optimized for a degree of longevity, to reduce buildupof debris, and/or other performance considerations.

Although read/write element array 400 includes R/W pairs 510, read/writeelement arrays may include only read elements or only write elements.For example, in the embodiment illustrated in FIG. 4, read/write elementarray 402 of module 212, and read/write element array 412 ofsupplemental module 230, include only read elements. Other embodimentsmay include different combinations read/write element arrays, to enable,for example, write-read-read (W-R-R) operations, R-R-W operations,read-after-write operations, etc. One skilled in the art will appreciatethat the concepts presented as applied to the embodiments disclosedwould apply to configurations other than those illustrated.

With specific regard to read element array 412 of supplemental module230, in various embodiments, read elements 414 may be constructed in thesame manner, generally described above, as read elements 408 inread/write arrays 400, 402, 404. However, read elements 414 need not beconstructed in the same manner as read elements 408, and thus need nothave the same performance characteristics. For example, read elementarray 412 of supplemental module 232 may be optimized for a specificgeneration of a tape medium. For example, read sensor width W_(R), andread sensor shield-to-shield spacing S_(SS), as illustrated on FIG. 5(and FIGS. 6A and 6B), may be optimized for track density, lineardensity (bits/inch), head-to-tape spacing, and/or other physical andmagnetic properties of a particular generation of tape, for example,LTO-6. In an exemplary embodiment, shield-to-shield spacing S_(SS) mayhave a nominal value of about 100 nm, and read sensor width W_(R) mayhave a nominal value of about 1-3 μm. More generally, theshield-to-shield spacing S_(SS) scales with the bit length, as is knownin the art, and the reader width may be in the range of 40-80 percent ofthe track width.

In various embodiments, meeting a particular nominal or other readsensor, read element, and/or read element array dimension, or otherconstruction characteristic, may be less important than knowing theactual dimensions or characteristics of the sensor, element, or array.For example, the magnetic field strength at a sensor is generallyproportional to the width of the read sensor, and decreasesexponentially with respect to the element-to-tape spacing. If the sensorwidth, tape spacing, and response and sensitivity curves of the readsensor are known, a very accurate magnetic field strength measurement ofthe tape transitions may be obtained from an analysis of the electricalsignals from the read sensor. In an embodiment, all read sensors in aread element array may be chosen to have substantially the samedimensions and/or characteristics through, for example, a binningprocess, or by physical measurements.

In addition to optimizing materials and construction of read elements414 for a specific generation of tape media, materials and constructionof the read elements maybe optimized for a desired performance. Forexample, materials and construction may be optimized for a level of readelement sensitivity, for a level of longevity, to reduce buildup ofdebris, and/or other performance considerations, with emphasis on one ormore of these performance characteristics.

For example, in certain embodiments, as illustrated in FIG. 6A, acoating 602 may be applied to a read element 414 of the supplementalmodule 230 during construction so as to force a defined separationbetween tape bearing surface 232, and thus sensor 502 of the readelement, and the tape. The separation will typically be a combination ofthe coating 602 depth plus the tape fly height over tape bearing surface232. In certain embodiments, as illustrated by FIG. 6B, sensor 502 maybe recessed a defined amount from tape bearing surface 232. The definedseparation may force an extra degree of spacing loss in the magneticfield strength detected by read elements 414 of read element array 412such that, for example, the signal resolution may be at or close to theminimum acceptable value, and may be used to detect sub-optimal, butwithin specification, performance of the read/write element arrays ofthe other read/write modules. In certain embodiments, coating 602 may bediamond-like carbon.

Based on the Wallace thickness loss response function, the magneticfield strength detected by a read element is proportional to e^(−kd/λ),where d is the element-to-tape separation, λ is the recordingwavelength, and k is a constant equal to 2πf/s, where f=recordingfrequency, and s=tape speed in recording. Thus, the detected magneticfield strength decreases exponentially both with respect to separationbetween the tape and the read element, and with respect to recordingdensity, which is inversely related to the recording wavelength λ. Basedon this relationship, a certain defined spacing can be implemented thatmay increase, or enhance, the spacing loss to force a certain BER or lowSNR at a relatively low degradation of write element performance.Threshold values can be defined for one or more performancecharacteristics related to write element 410 degradation that can bedetected by read elements 414, such that a detected performancecharacteristic above, or below, its related threshold value may indicatean unacceptable level of write element 410 degradation. In variousembodiments, defined spacings between 5-50 nm may be used. A definedspacing, or range of spacings, may be determined without undueexperimentation for a given tape media generation, a particular tapehead 118 and supplemental head 230 construction, and/or a specific setof data written to the tape.

As described above, motion control system 110 may periodically activate,for example, a servo that vertically moves supplemental module 230, or,in another embodiment, rollers or guides, that cause the supplementalmodule to engage tape 234. In various embodiments, motion control system110 may periodically cause the tape to engage the supplemental module,based on, for example, a duration that the tape drive is active, aspecific length or distance of tape that passes over read/write heads118, a number or a total duration of write operations performed by atape drive, each time a write operation is initiated on a newly mountedtape, a defined number of wraps of the tape around supply reel 122 ortake-up reel 124, or a combination of these. In general, motion controlsystem 110 may periodically cause the tape to engage the supplementalmodule often enough that significant degradation of the write elementsdoes not occur between each tape-to-supplemental head engagement, butnot so often that physical wear of the supplemental module shortens theperformance lifetime below a desired lifetime. In various embodiments,supplemental module 234 may engage tape 234 for a duration sufficientfor tape appliance 100 to read several blocks of data, for example, 3 to50 blocks.

In an embodiment, when motion control system 110 causes tape 234 toengage supplemental module 230, the signals generated by read elementarray 414, or corresponding information, may be transmitted tomicroprocessor controller 106. In an embodiment, microprocessorcontroller 106 includes firmware and/or software to process and analyzethe signals from read element array 414, and determine whether certainperformance characteristics of the write elements of read/write elementarrays 400, 402, 404, are within desired ranges. In other embodiments,microprocessor controller 106 may only process the signals from readelement array 414, and transmit the information to host CPU 102 forfurther analysis with regard to threshold values, by an analysisprogram, for example, one of application program(s) 828 (see FIG. 8)that may reside on host CPU 102. For example, read dataflow circuitry112 may perform a pre-processing function on the signals it receivesfrom each read element array, such as combining or averaging the signalsfrom all or some of the read elements in an array, before sending thisinformation to microprocessor controller 106. Similarly, microprocessorcontroller 106 may perform pre-processing or a degree of pre-analysisbefore sending signals and other information from the read elementarrays to host CPU 102. In certain embodiments, analysis may beperformed on aggregated signals from a read sensor array. In otherembodiments, analysis may be performed on signals from each read sensorof an array. When, for example, microprocessor controller 106 determinesthat a quality metric does not meet its associated threshold value, itmay, for example, transmit a warning message to host CPU 102.

For example, the amplitude of the signals from read element array 414may indicate the magnetic field strength of write elements 410 at tape234. An amplitude below a threshold value may indicate physical wear ofwrite elements 410, or may indicate a buildup of debris on the face of aread/write element array 400, 402, 404. Similarly, a low SNR in thesignals from read element array 414 may indicate similar degradation ofwrite elements 410.

When microprocessor controller 106 determines that a defined signalcharacteristic does not meet its associated threshold value, it may, forexample, transmit a warning message to host CPU 102 indicating thatoperator intervention may be required, or cause operations on the tapedrive to be suspended until the drive is reset.

While embodiments of the invention have been described with respect to atape appliance and a tape medium, those of skill in the art willrecognize that the inventive concepts described herein may beimplemented in embodiments directed to related magnetic storagetechnologies, without undue experimentation, and without departing fromthe spirit of the invention, and these are, therefore, considered to bewithin the scope of the invention, as defined in the claims below. Forexample, with respect to hard disk drive (HDD) technology, a specialpurpose set of heads may be constructed having read elements of varyingcharacteristics, as described above, for reading magnetic transitions ina data track in the magnetic media of an HDD platter. The same orsimilar quality metrics related to the magnetic transitions on theplatter, and the quality of the platter itself, may be determined, basedon established standards and specifications, and analysis of theelectrical signals generated by the read elements of the special purposeheads.

FIG. 7 is a flowchart depicting operational steps that microprocessorcontroller 106 may perform in determining whether a write element 410meets defined performance characteristics, in accordance with anembodiment of the invention. In an embodiment, microprocessor controller106 periodically issues a command signal to motion control system 110,which in turn sends a control signal to a servo controlling the verticalmovement of supplemental module 230, or, alternatively, to a servocontrolling a tape roller or guide, to cause the supplemental module toengage the tape (step 700). Microprocessor controller 106 receives theelectrical signals from, for example, read elements 414 of read elementarray 414 in tape bearing surface 232 of supplemental module 230 via acable 226 (step 702). Microprocessor controller 106 determines variousquality metric valuse based on the received electrical signals (step704). Microprocessor controller 106 then compares the quality metricvalues to threshold values or ranges (decision step 706). In certainembodiments, these quality metric values may be retained, for example,by host CPU 102, for historical analysis.

If microprocessor controller 106 determines that one or more performancecharacteristics are not within a desired range (decision step 706, “N”branch), then the microprocessor controller performs certain definedactions (step 708). For example, if certain key performancecharacteristic are not meeting a defined threshold value, a message maybe generated by microprocessor controller 106 and transmitted to hostCPU 102, via channel adapter 104, to indicate that operator interventionmay be required. Alternatively, microprocessor controller 106 maydisable writing to tape by modules 204, 212, and/or 208, until tapeappliance 100 is reset. Microprocessor controller 106 then issuescommand signals to cause supplemental module to disengage the tape (step708), and this processing ends until a defined period has elapsed,whereupon this processing begins again (step 700).

If microprocessor controller 106 determines that all performancecharacteristics are within their associated desired ranges (decisionstep 706, “Y” branch), then the microprocessor controller issues commandsignals to cause supplemental module to disengage the tape (step 710),and this processing ends until a defined period has elapsed, whereuponthis processing begins again (step 700).

FIG. 8 depicts a block diagram of components of host CPU 102, inaccordance with an embodiment of the present invention. It should beappreciated that FIG. 8 provides only an illustration of oneimplementation and does not imply any limitations with regard to theenvironments in which different embodiments may be implemented. Manymodifications to the depicted environment may be made.

Host CPU 102 can include one or more processors 802, one or morecomputer-readable RAMs 804, one or more computer-readable ROMs 806, oneor more computer-readable storage media 808, device drivers 812,read/write drive or interface 814, network adapter or interface 816, allinterconnected over a communications fabric 818. Communications fabric818 can be implemented with any architecture designed for passing dataand/or control information between processors (such as microprocessors,communications and network processors, etc.), system memory, peripheraldevices, and any other hardware components within a system.

One or more operating systems 810 and application program(s) 828 arestored on one or more of the computer-readable storage media 808 forexecution by one or more of the processors 802 via one or more of therespective RAMs 804 (which typically include cache memory). In theillustrated embodiment, each of the computer-readable storage media 808can be a magnetic disk storage device of an internal hard drive, CD-ROM,DVD, memory stick, magnetic tape, magnetic disk, optical disk, asemiconductor storage device such as RAM, ROM, EPROM, flash memory orany other computer-readable tangible storage device that can store acomputer program and digital information.

Host CPU 102 can also include a R/W drive or interface 814 to read fromand write to one or more portable computer-readable storage media 826.Application program(s) 828 on host CPU 102 can be stored on one or moreof the portable computer-readable storage media 826, read via therespective R/W drive or interface 814 and loaded into the respectivecomputer-readable storage media 808.

Host CPU 102 can also include a network adapter or interface 816, suchas a TCP/IP adapter card or wireless communication adapter (such as a 4Gwireless communication adapter using OFDMA technology). Applicationprogram(s) on host CPU 102 can be downloaded to the computing devicefrom an external computer or external storage device via a network (forexample, the Internet, a local area network or other, wide area networkor wireless network) and network adapter or interface 816. From thenetwork adapter or interface 816, the programs are loaded into thecomputer-readable storage media 808. The network may comprise copperwires, optical fibers, wireless transmission, routers, firewalls,switches, gateway computers and/or edge servers.

Host CPU 102 can also include a display screen 820, a keyboard or keypad822, and a computer mouse or touchpad 824. Device drivers 812 interfaceto display screen 820 for imaging, to keyboard or keypad 822, tocomputer mouse or touchpad 824, and/or to display screen 820 forpressure sensing of alphanumeric character entry and user selections.The device drivers 812, R/W drive or interface 814 and network adapteror interface 816 can comprise hardware and software (stored incomputer-readable tangible storage device 808 and/or ROM 806).

The present invention may be a system, a method, and/or a computerprogram product. The computer program product may include a computerreadable storage medium (or media) having computer readable programinstructions thereon for causing a processor to carry out aspects of thepresent invention.

The computer readable storage medium can be a tangible device that canretain and store instructions for use by an instruction executiondevice. The computer readable storage medium may be, for example, but isnot limited to, an electronic storage device, a magnetic storage device,an optical storage device, an electromagnetic storage device, asemiconductor storage device, or any suitable combination of theforegoing. A non-exhaustive list of more specific examples of thecomputer readable storage medium includes the following: a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), a static random access memory (SRAM), a portablecompact disc read-only memory (CD-ROM), a digital versatile disk (DVD),a memory stick, a floppy disk, a mechanically encoded device such aspunch-cards or raised structures in a groove having instructionsrecorded thereon, and any suitable combination of the foregoing. Acomputer readable storage medium, as used herein, is not to be construedas being transitory signals per se, such as radio waves or other freelypropagating electromagnetic waves, electromagnetic waves propagatingthrough a waveguide or other transmission media (e.g., light pulsespassing through a fiber-optic cable), or electrical signals transmittedthrough a wire.

Computer readable program instructions described herein can bedownloaded to respective computing/processing devices from a computerreadable storage medium or to an external computer or external storagedevice via a network, for example, the Internet, a local area network, awide area network and/or a wireless network. The network may comprisecopper transmission cables, optical transmission fibers, wirelesstransmission, routers, firewalls, switches, gateway computers and/oredge servers. A network adapter card or network interface in eachcomputing/processing device receives computer readable programinstructions from the network and forwards the computer readable programinstructions for storage in a computer readable storage medium withinthe respective computing/processing device.

Computer readable program instructions for carrying out operations ofthe present invention may be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, or either source code or object code written in anycombination of one or more programming languages, including an objectoriented programming language such as Smalltalk, C++ or the like, andconventional procedural programming languages, such as the “C”programming language or similar programming languages. The computerreadable program instructions may execute entirely on the user'scomputer, partly on the user's computer, as a stand-alone softwarepackage, partly on the user's computer and partly on a remote computeror entirely on the remote computer or server. In the latter scenario,the remote computer may be connected to the user's computer through anytype of network, including a local area network (LAN) or a wide areanetwork (WAN), or the connection may be made to an external computer(for example, through the Internet using an Internet Service Provider).In some embodiments, electronic circuitry including, for example,programmable logic circuitry, field-programmable gate arrays (FPGA), orprogrammable logic arrays (PLA) may execute the computer readableprogram instructions by utilizing state information of the computerreadable program instructions to personalize the electronic circuitry,in order to perform aspects of the present invention.

Aspects of the present invention are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer readable program instructions.

These computer readable program instructions may be provided to aprocessor of a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer readable program instructionsmay also be stored in a computer readable storage medium that can directa computer, a programmable data processing apparatus, and/or otherdevices to function in a particular manner, such that the computerreadable storage medium having instructions stored therein comprises anarticle of manufacture including instructions which implement aspects ofthe function/act specified in the flowchart and/or block diagram blockor blocks.

The computer readable program instructions may also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a series of operational steps to be performed on the computer,other programmable apparatus or other device to produce a computerimplemented process, such that the instructions which execute on thecomputer, other programmable apparatus, or other device implement thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

The flowchart and block diagrams in the figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof instructions, which comprises one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the block may occur out of theorder noted in the figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

Although preferred embodiments have been depicted and described indetail herein, it will be apparent to those skilled in the relevant artthat various modifications, additions, substitutions and the like can bemade without departing from the spirit of the invention, and these are,therefore, considered to be within the scope of the invention, asdefined in the following claims.

1. An apparatus comprising: a production module that is substantially inconstant engagement with a magnetic tape recording medium, theproduction module including at least one write element that writesmagnetic transitions to the magnetic tape; a supplemental module,including at least one read element, that periodically engages themagnetic tape, whereby the read element generates an electrical signalcorresponding to the transitions written to the magnetic tape by the atleast one write element, the read element disposed a distance away fromthe tape when the supplemental module engages the tape such that asignal resolution measurement value is approximately a minimumacceptable value when the tape is a reference tape; a computer thatreceives information representative of the electrical signal anddetermines if a quality metric of the magnetic tape derived from theelectrical signal is within a defined range; and in response todetermining that the quality metric is not within the defined range,performing a defined action.
 2. An apparatus in accordance with claim 1,further comprising a servo coupled to the supplemental module, whereinactivating the servo engages or disengages the supplemental module fromthe magnetic tape recording medium, independent of the productionmodule.
 3. An apparatus in accordance with claim 1, further comprising atape roller or guide coupled to a servo, wherein activating the servocauses the tape roller or guide to engage or disengage the magnetic tapefrom the supplemental module.
 4. An apparatus in accordance with claim1, wherein the quality metric is one or more of: transition magneticfield strength at one or more bit densities, signal-to-noise ratio(SNR), transition parameter, PW-50 pulse width, bit error rate (BER),degree of overwrite.
 5. (canceled)
 6. An apparatus in accordance withclaim 1, wherein the supplemental module includes a coating disposedover the read element having a thickness sufficient to cause the readelement to be disposed the distance away from the magnetic tape when thesupplemental module engages the magnetic tape.
 7. An apparatus inaccordance with claim 1, wherein the read element is recessed from amagnetic tape bearing surface of the supplemental module sufficient tocause the read element to be disposed the distance away from themagnetic tape when the supplemental module engages the tape.
 8. Anapparatus in accordance with claim 1, wherein the distance away from thetape magnetic is approximately between 5 and 50 nm.
 9. An apparatus inaccordance with claim 1, wherein the supplemental module periodicallyengages the magnetic tape one or more of: once per a defined number ofwraps of the tape around a supply reel or take up reel, after a definedelapsed tape recording appliance operation time, after a defined tapelength that moves across the tape head module, when a tape is loaded tothe tape recording appliance, when a BER exceeds a threshold value. 10.An apparatus in accordance with claim 1, wherein the supplemental moduleperiodically engages the magnetic tape recording medium sufficient forthe supplemental module to read a defined number of data blocks from themagnetic tape recording medium.
 11. An apparatus in accordance withclaim 1, wherein the defined action is one or more of: transmitting amessage signal indicating that the quality metric is not within thedefined range, and disabling write operations by the write head.